Nitrogen concentration effect on maximal diffusive methane flux from sediments...

Nitrogen concentration effect on maximal diffusive methane flux from sediments is added to simple methane model

source/Flake/flake_methane.f90

@@ -29,7 +29,15 @@ real(kind=ireals), parameter :: Henry_const0_ch4 = 1.3d-5   !> Henry constant fo
 real(kind=ireals), parameter :: Henry_temp_dep_ch4 = 1.7d+3 !> The temperature dependence of Henry constant for methane, K
 real(kind=ireals), parameter :: Henry_temp_ref = 298.15     !> The reference temperature for Henry constants, K
 real(kind=ireals), parameter :: Henry_const0_o2 = 1.3d-5    !> Henry constant for oxygen at the reference temperature, mol/(m**3*Pa)
+real(kind=ireals), parameter :: Henry_const0_n2 = 6.2d-6    !> Henry constant for nitrogen at the reference temperature, mol/(m**3*Pa)
 real(kind=ireals), parameter :: Henry_temp_dep_o2 = 1.7d+3  !> The temperature dependence of Henry constant for oxygen, K
+real(kind=ireals), parameter :: Henry_temp_dep_n2 = 1.3d+3  !> The temperature dependence of Henry constant for nitrogen, K
+
+real(kind=ireals), parameter :: n2_atm0 = 4.96d-1  !> Concentration of nitrogen in water, in equilibrium with
+                                                   !> atmospheric partial nitrogen pressure (80046 Pa), 
+                                                   !> according to Henry law with reference constant, mol/m**3
+real(kind=ireals), parameter :: n2_exp_decay = 5.  !> The decay rate in exponential law for nitrogen conecntration in soil, m**(-1)
+                                                   !> 50. in (Bazhin, 2001)
 
 
 real(kind=ireals), parameter :: molm3tomgl_o2 = 32.
@@ -177,6 +185,7 @@ real(kind=ireals) :: C_b                   !> Methane concentration at the lake
 real(kind=ireals) :: C_O2_ML               !> Oxygen concentration in the mixed layer, mol/m**3
 real(kind=ireals) :: C_O2_hypo             !> Oxygen concentration in the hypolimnion, mol/m**3
 real(kind=ireals) :: C_CH4_Henri           !> Henry constant for methane, mol/(m**3 * Pa)
+real(kind=ireals) :: C_N2_Henry            !> Henry constant for nitrogen, mol/(m**3 * Pa)
 real(kind=ireals) :: F_difbot              !> Bottom diffusive flux of methane, mol/(m**2*s)
 real(kind=ireals) :: Prod                  !> Methane production in bottom sediments, mol/(m**2*s)
 real(kind=ireals) :: CH4ppb                !> Atmospheric methane concentration, ppb
@@ -236,7 +245,9 @@ if     (model == 1) then
   F_difbot = k_ * (C_b * cos1 - C_ML) / sin1
 elseif (model == 2) then
   diffsoil = tortuosity_coef * DIFF_WATER_METHANE( Tb )  
-  F_difbot = min(Prod, diffsoil * por * C_CH4_Henri * gammas * rhosoil * g)
+  C_N2_Henry = HENRY_CONST(Henry_const0_n2, Henry_temp_dep_n2, Henry_temp_ref, Tb)
+  F_difbot = diffsoil * por * C_CH4_Henri * gammas * (rhosoil * g + n2_atm0 * n2_exp_decay / C_N2_Henry)
+  F_difbot = min(Prod, F_difbot)
   C_ML = (F_difbot + gas_exch_const * meth_atmo * cos1) / &
        & ( (gas_exch_const + meth_oxid_const_ML * h_ML_eff) * cos1  + k_* sin1)  
 endif